Production of metallic compacts



April 23, 1968 J. E. ELLIOTT ETAL 3,379,525

PRODUCTION OF METALLIC COMPACTS Filed Jan. 25, 1961 Inventors JIM-IN E ELL a 7' HLAN R MonRELL United States Patent 3,379,525 PRODUCTION OF METALLIC COMPACTS John Eric Elliott and Alan Paylor Morrell, London, England, assignors to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed Jan. 23, 1967, Ser. No. 610,890 3 Claims. (Cl. 75221) ABSTRACT OF THE DISCLOSURE This invention provides for a method of manufacturing metallic compacts by presintering loose nickel-iron magnetic powder in a mold that has a base plate with a smooth inner surface of a refractory material of the group consisting of borosilicate glass and silica, then further sintering the formed compact in a furnace. The smooth inner surface of refractory material greatly reduces the friction between the compact and the mold thereby insuring that the metal compact would be crack free after the presintering operation is completed.

The invention relates to a method for producing sintered metal compacts.

For the production of metallic strip from metal powders it is desirable first to form a regular compact from the powdered metal, which may then be cold-rolled to a desired thickness and cut at desired lengths. Compacts may be formed by compressing powder into the form of a block and then consolidating the so formed bldck by a sintering heat treatment. Alternatively compacts may be formed by one or more processes of heating powder in a container of suitable dimensions without pressure until a coherent compact is formed.

According to the present invention there is provided a method of manufacturing a metal compact which includes the step of heating a metallic powder in a reducing atmosphere in a container having at least a base inner surface of refractory material, to a temperature below the melting point of the said material and subsequently sintering the product so formed.

In one embodiment of the invention the material is borosilicate glass, and in another embodiment the material is silica.

The foregoing and other features according to the invention will be apparent from the following description of an embodiment thereof taken in conjunction with the accompanying drawings in which:

FIG. 1 shows in longitudinal cross-section a container for heat treating metal powders; and

FIGS. 2 and 3 show in longitudinal cross-section the container and contents after successive stages in the production of a metallic compact.

With reference to FIG. 1 the container has side members of mild steel, each with a flange 11 containing screw threads 12, and an outer base plate 13 of mild steel having screw threads 14 at corresponding positions to those in the flange. The base plate 13 supports an asbestos sheet 15 of reduced size, and a smooth commercially obtained borosilicate glass plate 16, both of slightly smaller measurements such that when the screws 17 are in position the side members 10 fit flush with the perimeter surface of the borosilicate glass plate. The container may be constructed to a desired size; for practical convenience it is desirable to obtain compacts of approximate size 2 feet long 9 inches wide and 1 inch thick, thickness being critical for rolling purposes. In these circumstances a practical realization of the size of the container would be no more than 2 or 3 inches in excess of the said measurements, the desired size depending upon the shrinkage characteristics of the powder to be sintered.

For the preparation, for example, of nickel-iron magnetic strip a desired amount of high purity nickel and iron powders 18 of typical particle size 5 microns are weighed, tumbled to ensure thorough particle blending and placed in the container (FIG. 2).

The powder is then pre-sintered in hydrogen at a temperature of the order of 500 C. for approximately three hours during which time the powder sinters and shrinks to form a coherent compact. An approximate figure for linear shrinkage during pre-sinten'ng is 5%; and normally it is during this operation that the compact so forming is prone to cracking by virtue of the forces of friction, predominantly along the base of the container and to a minor extent along the sides of the container. By the use of a smooth borosilicate glass as a base plate friction is greatly reduced so that compacts obtained after the first sintering operation are crack free.

The compact 22 (FIG. 3) so formed is then transferred to a furnace at a higher temperature where it is sintered in an atmosphere of hydrogen and at a temperature approaching the melting point. The compact is then removed, cold rolled and cut to a desired thickness and length to provide nickel-iron magnetic strip.

The method is particularly, although not exclusively suitable for the production of magnetic strip. An advantage of the invention is that when sintering powders, particularly those having high shrinkage characteristics, metallic compacts may be obtained with good mechanical properties, the use of borosilicate glass providing a smooth surface and offering a negligible frictional force, such that compacts are less prone to develop cracks whilst in formation.

As an alternative material to borosilicate glass, silica may be used. A plane of silica provides the requisite smooth surface and offers a negligible frictional force to the powdered material.

The invention resides also in piece parts produced from material prepared according to the invention.

While the principles of the invention have been described in connection with specific embodiments it is to be clearly understood that this description is made by way of example and not as a limitation on the scope of the invention.

\Ve claim:

1. In the method of making a body of sintered nickeliron magnetic powders wherein the powders are placed in a mold, presintered and then sintered, the improvement comprising using as the base plate of the mold a smooth inner surface of a refractory material of the group consisting of borosilicate glass and silica.

2. A method as claimed in claim 1 wherein the base inner surface is of borosilicate glass.

3. A method as claimed in claim 1 wherein the base inner surface is of silica.

References Cited UNITED STATES PATENTS 3/1940 Howe --200 X 3/1948 Richardson 18-47 OTHER REFERENCES CARL D. QUARFORTH, Primary Examiner. R. L. GRUDZIECKI, Assistant Examiner. 

